1. Field of the Invention
The present invention relates to a control system for a cable crane transporting a concrete in a dam construction site or so forth, for realizing automatic operation.
2. Description of the Related Art
As is well known, a cable crane has been employed as one of means for transporting a concrete from a preparing site to a casting site, such as in a dam construction site or so forth.
As shown in FIG. 24, the cable crane includes a main cable 2 stretched above a dam 1 to be constructed between mountains, between slopes, a trolley 3 suspended from the main cable and capable of traveling there along, a traction cable 4 for driving the trolley 3, a concrete bucket 6 hanging below the trolley 3 via a hanging cable 5, a transverse winch 7 for driving the traction cable 4 to reciprocally travel the trolley 3 between a transportation start position A at the mountain side and a transportation end position B at a desired position on the bottom of dam, and a vertical winch 8 for extracting and retracting the hanging cable 5 for lifting up and down the bucket 6. In an operation room 9, the position of the trolley 3 and the position of the bucket 6 are monitored for operating respective winches 7 and 8.
At the upper side portion of the transportation start position A, a transporting carrier 10 is traveling in a direction perpendicular to the plane of the drawing for transporting a concrete prepared by a not shown batcher plant. On the other hand, a concrete hopper 11 is arranged at the transportation end position B. The trolley 3 is driven to transversely travel along the main cable 2 according to a control signal from the operation room 9, and in conjunction therewith, the bucket 6 is lifted up and down by the hanging cable 5 by the control signal, in order to position the bucket 6 at respective positions A and B. At the position A, the concrete is supplied to the bucket 6, and at the position B, the concrete is discharged from the bucket 6.
In case of a large scale construction, such as dam, a huge amount of concrete is required. Therefore, in order to shorten the construction period and to reduce the construction cost, it is required to minimize the period required for transporting concrete by the bucket 6 in each transportation cycle. Therefore, as shown by arrow in FIG. 24, it is desirable to move the bucket 6 between the positions A and B through a path of a minimal distance.
In the cable crane, the magnitude of displacement of the trolley 3 in the transverse direction and the magnitude of displacement of the bucket 6 in the vertical direction can be derived on the basis of extraction amounts of the traction cable 4 and the hanging cable 5 and deflection magnitude of the main cable 2 depending upon the weight loads of the trolley 3, the bucket 6 and the concrete to be transported, from time to time. Accordingly, by deriving a coordinate of the bucket 6 with respect to a certain reference point, such as the transportation start position A, and by commanding forward and reverse rotation, acceleration and deceleration or stopping on the basis of the coordinate of the bucket 6 derived as set forth above. Thus, the bucket 6 may be automatically operated along the predetermined minimum distance.
However, in the case of the foregoing method, in which the instantaneous bucket position is measured in a real time on the basis of the extraction amount of the main cable 2 or so forth and the load on the bucket or so forth for moving the bucket 6 along an optimal traveling path, a time lag may be caused for transmitting necessary control information for driving the bucket 6 along the optimal traveling path to winch drive control system since it will take a certain period for deriving the position of the bucket 6. This practically causes difficulty in driving the bucket 6 along the optimal traveling path. If the driving speed of the winches are lowered so that the control information can be derived in time, it should take longer period than that of the case where the movement of the bucket 6 is manually controlled by an operator to cancel merit of the automatic control. Furthermore, in acceleration and deceleration of the winches, swing (pitching) motion of the bucket 6 is potentially induced due to inertia moment exerted on the bucket 6. For precisely positioning the bucket 6, it becomes necessary a control for suppressing the swing motion of the bucket 6.
Conventionally, automatic control is performed until the bucket 6 reaches the position in the vicinity of the position A or position B as the starting point or the destination point, and in the area near each position A and B, the bucket 6 is operated manually for suppressing swing motion and positioning at the desired point by the operator in the operation room 9 through radio communication with monitoring staff acting at each position A and B and in accordance with the instructions from the monitoring staff.
However, in this method, the qualified staff have to be arranged at each position A and B for providing proper instructions to the operator. In addition, actual fine adjustment on the basis of exchanging of information between the monitoring staff and the operator should cause a substantial delay. Furthermore, the control direction and control magnitude to be provided to the drive control system for the winch tends to be vague. Accordingly, whether the bucket can be positioned within a short period or not mainly depends on the degree of skill of the operator and the monitoring staff. Furthermore, due to manual operation, it cannot be certain whether the transporting operation can be completed within a given period in every transporting operation.
In addition, when the bucket is placed near the position A or B, the workers must move away for avoiding inadvertent accident to cause lowering of working efficiency.